I believe that the main argument in Marquis argumentation start with the fact that inherently all human beings have a “future of value”. And your argumentation is that all you need in order to obtain this “future of value” is food and water etc.
I would argue that first, we have no means of determining or evaluating what a valuable future might be for an individual, as the question of value is established individually based on past experiences. The fact that a fetus has no conscient previous experience makes it impossible to establish the value in it’s future.
Secondly I would argue that, considering that we establish a commonly agreed standard of a valuable life, an almost impossible task, given the immensity of contradictory lifestyles and cultures, lifestyles that if all geo-social, climateric conditions occur, still might lead in some cases to a purely unhappy and unfulfilled life, still acheiving that valuable future is a direct consequence of the willingness of the mother to engage in the lenghty process of more than 5–10 years of caring and loving that human being. A future by mediocre standards in the western society needs much more than just organic matter being fed to the offspring.
Base point is that if at least the mother is not willing to commit to the task of providing that valuable future, the perspective of it is highly diminshed.